The invention relates to a holder for a ball-headed end of a tappet, in particular of a piston rod of a motor vehicle brake cylinder, the holder and the ball head being a pair of components of a ball-and-socket joint which couples a translational movement of the tappet to a rotational movement of a component connected to the holder, in particular of a pedal arm of a brake pedal.
Holders of this type are required, for example, in order to connect the pedal lever of a brake pedal to the ball head of a brake cylinder in an articulated manner and to reliably transmit the pedal force to the tappet. For this purpose, the ball head is inserted into a ball socket which surrounds the ball head over more than 180xc2x0, making an articulated connection possible. In this case, the ball head forms a non-releasable unit with the tappet and the cylinder and for this reason the ball socket has to be designed such that it can be divided or deformed elastically in such a manner that the ball head can be clipped into the ball socket.
Divided ball sockets require an undesirably high outlay on installation. A disadvantage in the case of elastic holders of this type is that the connection between the holder and the ball head can be forcibly separated when a maximum permissible force is exceeded. Firmly clamping the ball head in order to avoid this danger restricts the mobility of the ball head in an undesirably severe manner. A further disadvantage is that the vibrations caused by the engine are transmitted by the ball head to the holder and over the long term lead to wear there and therefore also to play in the force transmission. This has, however, to be avoided for safety reasons, particularly in brake systems, and so in this case the replacement of the affected components is required.
The invention is based on the problem of configuring a holder for a ball head in such a manner that said holder operates reliably and in a manner which is largely free of wear and at the same time can be fitted in a simple manner.
According to the invention, this problem is solved by the holder comprising a cup-shaped hollow body and an elastic insert body arranged within the hollow body, and by the ball head being held in the interior of the hollow body by the insert body by means of a securing means and being prestressed against the base of the hollow body.
By this means, the ball head is fixed by the insert body in such a manner that it is not possible for the ball head to slip out even when subjected to a high load or only by destruction of the securing means. The applied force is therefore reliably transmitted via the holder and the insert body to the ball head and from there, for example, to the tappet of the brake cylinder. At the same time, the design of the insert body as an elastic element, for example elastomer, ensures that vibrations caused in a motor vehicle primarily by the drive and introduced into the holder via the ball head are largely absorbed.
In this connection, a development of the invention is particularly advantageous in which the holder has a further insert body arranged in the hollow body, so that the ball head is fixed between the two insert bodies in the hollow body by means of the securing means. This enables a particularly secure and permanent fixing of the ball head in the holder to be achieved. To this end, the second insert body can be designed, for example, as a sintered component. In this design, the ball head preferably bears against the two insert bodies, which means that a special configuration of the inner surface of the hollow body corresponding to the contour of the ball head can be omitted.
An advantageous development of the invention is provided if the ball head is enclosed in a sealing manner by the two insert bodies. The penetration of dirt particles or moisture is effectively avoided as a result. The wear to the ball head is thereby reduced and therefore the working life of the holder increased. Furthermore, lubricants are prevented from escaping, which means that complicated maintenance work is not needed.
The stated problem is solved especially well, in particular with a further embodiment in which at least one insert body has a recess forming a lubricant magazine. This makes it possible for the quantity of lubricant available for lubricating the ball head, and therefore the working life of the bearing, to be increased.
An advantageous embodiment is provided if the ball head is surrounded over approximately 180xc2x0 by the insert body. This facilitates the insertion of the ball head into the insert body by the insert body forming a half shell.
The insert body can be divided in a plane lying parallel to the plane which is described by the tappet connected to the ball head. In contrast, another advantageous embodiment is provided by the elastic insert body being provided with an opening which is designed elastically such that in the fitted state it bears against the tappet connected to the ball head, and for installation purposes can be stretched sufficiently far that the ball head can be passed through it. This makes an integral embodiment of the insert body possible. As a result, the use of non-releasable units consisting of a ball head, tappet and cylinder is substantially simplified.
The stretching, required for this, of the insert body is possible in a particularly easy manner if the elastic insert body has a radial constriction on its circumference. By this means, essentially two advantages can be achieved. Firstly, because of the reduction in material thickness the constriction makes it easier to stretch, which simplifies the passing through of the ball head. Secondly, the insert body can be easily compressed and is placed uniformly against the surface of the ball head, as a result of which a compensation of tolerances is also provided at the same time.
In this case, a particularly simple embodiment of the invention is provided if the hollow body is designed as a hollow cylinder closed on one side. The hollow cylinder provided in such a manner, for example, with a cover can thereby easily be provided, on the one hand, with a fastening element for connection to further components. On the other hand, the design of the holder as a hollow cylinder closed on one side improves the stability and durability of the holder. Furthermore, the closed end of the hollow cylinder can serve as an abutment for the securing means, which thus fixes the ball head in the hollow cylinder.
This can take place by means of a particularly advantageous development in which the hollow body has a recess which is designed as a quarter-turn fastener and is designed for fixing the inserted securing means in the hollow body.
For this purpose, the hollow body merely has a correspondingly shaped recess in its circumferential surface, so that the securing means, which is inserted into the hollow body counter to the restoring force of the elastic insert body, is secured in a positive-locking manner in the recess by a rotational movement. To this end, the securing means is provided with at least two extensions projecting over the inner width of the hollow body. As a result this embodiment is favorable to produce and can be fitted or removed easily.
It may be desirable, depending on the use, to individually adapt the tension of the insert body surrounding the ball head. This could be done by replacing an insert body for an insert body having different external dimensions and/or different material properties. However, a development of the invention is particularly advantageous for this in which the quarter-turn fastener is designed for holding additional securing means.
In this connection, with each additional securing means the remaining gap is reduced and the tension of the insert bodies increased. The manufacturing tolerances can therefore be kept relatively large and the adaptation to the ball head can be undertaken during installation by differing the number of securing means. Furthermore, the slackening of the restoring force of the elastic insert body over the working life of the holder can be compensated for in an identical manner without requiring the replacement of the existing insert body for this. In this connection, the holder does not need to be opened in order to insert further securing means, and so dirt is unable to penetrate during the adaptation.
A favorable development of the invention is provided if the securing means is a spring plate. In this case, the tension transmitted to the insert body can be preset by selection of a suitable securing means having a corresponding spring force. The elasticity of the elastic insert body accordingly essentially serves to absorb vibrations, the tension for fixing the ball head being introduced by the spring plate.
The securing means could be arranged laterally next to the ball head. In order to compensate for the non-uniform distribution of forces resulting therefrom, further securing means would then have to be provided. A particularly advantageous embodiment ensures a uniform distribution of force if the securing means has an opening for passing the ball head through it. This enables a uniform transmission of the introduced force from the insert body to the ball head to be achieved.
In this connection, it has proven particularly advantageous if the securing means has sections which are designed as detent pawls and permit the ball head to be passed through in only one direction. By this means, a further improvement in operating safety can be ensured, since, when the ball head is wrenched out of its holder, the detent pawls are plastically deformed beforehand and considerable forces are required for this. At the same time, the installation of a securing means designed in such a manner can be further simplified.
A development of the invention is particularly advantageous in which the holder is arranged on a lever and engages in a connecting element which is designed to absorb the forces which are not axial with respect to the tappet. By this means, the holder can be relieved of forces which are, for example, produced during the pivoting movement because of the change in angular position between the tappet and the lever, and act transversely to the pivot axis. For this purpose, the forces which are not axial are absorbed by the connecting element and the bearing of the lever is relieved of load as a result.
It is particularly favorable for this if the lever and the connecting element are arranged such that they can pivot about a common axis. By this means, the connecting element and the lever execute the same movement with only the axial forces being absorbed by the lever. This relieves the load on the bearing of the lever, at the same time making unrestricted movement of the lever possible.